1. Field of the Invention
The present invention relates to a numerical controller for controlling a machine, such as a machine tool or industrial machine, and more particularly, to a numerical controller for a machine having a component inspection timing notification function capable of notifying a user of the timing for component inspection.
2. Description of the Related Art
Machines, such as machine tools and industrial machines, use a large number of components that require periodic inspections and should be replaced immediately if their life is determined to be exhausted. However, it is difficult to control inspection timings for all the components. There are some techniques to overcome this. A machine maintenance inspection guide described in Japanese Patent Application Laid-Open No. 2-173803 is used to notify a user of the necessity of component inspection when reference values for inspection are exceeded by integrated values of the operating time of machine and frequency of machine usage. Further, an equipment inspection guide display method described in Japanese Patent Application Laid-Open No. 10-320031 and a maintenance management device and system for a machine tool described in Japanese Patent Application Laid-Open No. 2004-334507 are techniques for determining the next scheduled date of inspection based on a predetermined inspection cycle and notifying a user of it. If notified of the necessity of inspection, a user measures state quantities (voltage, insulation resistance value, deformation, frequency, etc.) for the determination of the life of a component. If reference values for the determination of the component life are exceeded by the measured values, the component life is determined to be exhausted and the component is replaced with a new one.
However, the prior art techniques have the following problems.
A “first problem” is that the component inspection is performed periodically. Some of the state quantities measured during the inspection do not change at a constant rate. If the component is a brand-new one, some state quantities change gradually at first and then drastically after continuous use for a fixed period of time. If the inspection cycle is fixed, the determination of the component life based on these state quantities is subject to the following problems.
First, in a period during which the state quantities gradually change, the inspection is repeated in vain despite the scarcity of the change if the inspection cycle is short. In a period during which the state quantities drastically change, in contrast, the component life may be exhausted before the inspection is performed if the inspection cycle is long. To avoid this, in this case, reference values possibly must be set at which a serviceable component is unduly determined to be exhausted. Thus, it is inefficient to periodically perform the component inspection.
A “second problem” is that it may not be efficient to perform the component inspection immediately after a user is notified of the necessity of the inspection. Machining of products by means of a machine tool requires a plurality of processes and such a production schedule that a predetermined number of products can be efficiently machined until the appointed date of delivery. If the machine tool is unexpectedly stopped, therefore, the production possibly must be rescheduled thereafter, and this rescheduling work is time-consuming. Further, some machines incorporated in production lines cannot be easily stopped.